1. Field of the Invention
The present invention relates to an electrode structure for a plasma display panel (PDP) and, more particularly, to an electrode structure to be provided in each cell of a PDP.
2. Description of the Related Art
A conventional PDP cell structure will first be described in connection with a surface discharge PDP having paired display electrodes (primary electrodes) provided on a substrate for light emission.
FIG. 35 is a perspective view illustrating a part of a common AC-driven three-electrode surface discharge PDP for color display.
As shown, the PDP includes a front panel assembly and a rear panel assembly. The front panel assembly includes a front glass substrate 11, pairs of display electrodes X, Y arranged parallel to each other on the front substrate 11 for surface discharge, and a dielectric layer 17 of a glass material provided over the display electrodes. A protective film such as of MgO (not shown) is provided on the dielectric layer 17. The display electrodes X, Y each include a transparent electrode 12 such as of ITO and a bus electrode 13 of a metal.
The rear panel assembly includes a rear glass substrate 21, address electrodes (signal electrodes) A arranged perpendicularly to the display electrodes X, Y on the rear substrate 21, barrier ribs 29 provided between the address electrodes A and A for partitioning a discharge space, and red, green and blue fluorescent layers 28R, 28G and 28B provided between the barrier ribs 29.
The rear panel assembly and the front panel assembly are combined in an opposed relation with the periphery thereof sealed, and the discharge space defined therebetween is filled with a discharge gas. Intersections between the paired display electrodes X, Y and the address electrodes A each define a discharge region of a unit light emitting cell. The pairs of display electrodes X and Y each define a display line therebetween. Each pixel includes three unit discharge sections (sub-pixels), i.e., RGB unit discharge sections, arranged in juxtaposition. Therefore, the RGB unit discharge sections are arranged in a grid pattern in the PDP.
The display electrodes X, Y are generally referred to as xe2x80x9cprimary electrodesxe2x80x9d or xe2x80x9csustain electrodesxe2x80x9d, because they serve to induce a primary discharge and to sustain light emission in the PDP. For convenience of explanation, the transparent electrodes 12 of the display electrodes X, Y are herein referred to as xe2x80x9cbranch electrodesxe2x80x9d.
FIG. 36 is a diagram illustrating the unit discharge sections of the PDP of FIG. 35 arranged in a grid pattern as viewed in plan, and FIG. 37 is a diagram illustrating a positional relationship between the unit discharge sections and the display electrodes of the PDP of FIG. 35 as viewed in plan.
As shown in FIG. 36, the unit discharge sections K of the PDP each have a rectangular shape, and are arranged in a grid pattern. Discharge gaps are respectively provided in the unit discharge sections K as viewed in plan. In some cases, the unit discharge sections K are arranged in a special configuration (e.g., a delta configuration), but generally each correspond to an R, G or B minimum light emitting unit (sub-pixel). Each set of RGB unit discharge sections are arranged in a square or generally square configuration, so that the unit discharge sections K each have a vertically elongated rectangular shape.
As shown in FIG. 37, the discharge space is generally partitioned on a column-by-column basis by the barrier ribs 29 to provide discharge regions H within the respective unit discharge sections as viewed in plan. Therefore, the discharge regions in the unit discharge sections each have a further smaller width. That is, the discharge regions H are each defined as a region provided by excluding barrier rib regions from the unit discharge section K.
As viewed in plan, the discharge gaps D are each defined as a slit between the branch electrodes 12 of the display electrodes X and Y. A space defined between the bus electrodes 13 of the paired display electrodes X, Y is generally referred to as a reverse slit (or a non-discharge slit).
FIG. 38 is a diagram illustrating an electrode structure of the PDP of FIG. 35 as viewed in plan. In FIG. 38, the barrier ribs 29 are located in non-discharge regions. As described above, the discharge regions H are provided by excluding the barrier rib regions (non-discharge regions) from the unit discharge sections K.
In such an electrode structure, the discharge gaps D each have a relatively small gap length L, so that the discharge is concentrated in the discharge gaps. Therefore, the protective film in the discharge gaps are liable to be deteriorated. For this reason, the gap length of the discharge gaps is increased by skewing the discharge gaps with respect to a row of the unit discharge sections, as disclosed in Japanese Unexamined Patent Publication No. 9-231907 (1998).
FIGS. 39 and 40 are diagrams illustrating exemplary electrode structures in which the discharge gaps are skewed with respect to the unit discharge sections.
As shown, the gap length L of the discharge gaps D in the electrode structures is increased for prevention of the partial deterioration of the protective film. Another electrode structure with skewed discharge gaps is disclosed in Japanese Unexamined Patent Publication No. 2000-195431.
It is known that the luminous intensity on an electrode increases toward a discharge gap (see, for example, T. Yoshioka, et al., xe2x80x9cCharacterization of Micro-Cell Discharge in AC-PDPs by Spatio-temporal Optical Emission and Laser Absorption Spectroscopyxe2x80x9d, Proc. of IDW ""99, 603(1999)). If the electrode is provided apart from the discharge gap in the discharge region, the luminous intensity on the electrode is reduced, resulting in a lower luminous efficiency.
In the electrode structure shown in FIG. 39, the width of each branch electrode 12 extending from a bus electrode 13 is varied along the length of the branch electrode for provision of a skewed discharge gap D, so that a greater width portion of the branch electrode has an area remote from the discharge gap D.
In the electrode structure shown in FIG. 40, each branch electrode 12 has branch portions in a discharge region for provision of a skewed discharge gap D, so that one of the branch portions of the branch electrode 12 extends apart from the discharge gap D. Therefore, the branch electrode has an area remote from the discharge gap D.
In view of the foregoing, the present invention is directed to an electrode structure for a plasma display panel, in which a pair of branch electrodes having a generally constant width but no branch portion in a discharge region respectively extend from bus electrodes to define a skewed discharge gap therebetween, so that the branch electrodes do not have an area remote from the discharge gap, thereby preventing the reduction of the luminous intensity for improvement of the luminous efficiency.
In accordance with the present invention, there is provided an electrode structure for a plasma display panel having a plurality of unit discharge sections arranged in a matrix array in a discharge space defined between a pair of substrates, the electrode structure comprising a pair of bus electrodes, and a pair of branch electrodes respectively extending from the bus electrodes in each of the unit discharge sections to define a discharge gap therebetween, wherein the bus electrodes each extend along a row of the matrix array of the unit discharge sections, wherein the branch electrodes each have a generally constant width and obliquely extend across a discharge region in each of the unit discharge sections so that the discharge gap defined between the branch electrodes is skewed with respect to a column of the matrix array of the unit discharge sections.
With this arrangement, the branch electrodes each have a generally constant width and obliquely extend across the discharge region in the unit discharge section, so that the discharge gap defined between the branch electrodes respectively extending from the bus electrodes are skewed with respect to the column of the matrix array of the unit discharge sections. Therefore, the branch electrodes do not have an area remote from the electrode gap, thereby preventing the reduction of the luminous efficiency for improvement of the luminous efficiency.